1. Field of the Invention
The present invention relates to a spindle motor and a disk drive apparatus.
2. Description of the Related Art
Spindle motors arranged to rotate disks are installed in hard disk drives. A conventional hard disk drive and a conventional spindle motor are described, for example, in JP-A 2006-040423. Paragraph [0032] of JP-A 2006-040423 states that the spindle motor (SPM) is fixed to a base of a hard disk drive (HDD). In addition, paragraph [0065] of JP-A 2006-040423 states that a low-density gas having a lower density than that of an air, such as He, is used as an atmosphere inside a hard disk assembly (HDA).
A case of the hard disk drive is arranged to be substantially airtight in order to keep an interior space thereof clean. In particular, the low-density gas, such as He, tends to easily pass through even a minute gap. Therefore, in the case where an interior of the case is to be filled with the low-density gas, as in JP-A 2006-040423, extreme airtightness is required. In order to improve the airtightness of the case, it is desirable that the number of through holes defined in a base thereof should be decreased.
Meanwhile, a bearing mechanism arranged to support a rotating portion of the spindle motor is fixed to the base of the hard disk drive. In order to fix the bearing mechanism without providing a through hole in the base, it is conceivable, for example, to provide a cup portion having a bottom and being cylindrical in the base, and insert the bearing mechanism in the cup portion. However, when the bearing mechanism is inserted into the cup portion having the bottom and being cylindrical, resistance against insertion of the bearing mechanism into the cup portion may be increased because a gas cannot travel downward out of the cup portion. This will decrease efficiency in an assembling operation and make it difficult to accurately position the bearing mechanism with respect to a base member.